Apparatus and method for image coding based on filtering

This application is a continuation of U.S. application Ser. No. 17/639,262, filed on Feb. 28, 2022, which is a National Stage application under 35 U.S.C. § 371 of International Application No. PCT/KR2020/011591, filed on Aug. 31, 2020, which claims the benefit of U.S. Provisional Application No. 62/893,754, filed on Aug. 29, 2019. The disclosures of the prior applications are incorporated by reference in their entirety.

The present disclosure relates to a apparatus and method for image coding based on filtering

Recently, demand for high-resolution, high-quality image/video such as 4K or 8K or higher ultra high definition (UHD) image/video has increased in various fields. As image/video data has high resolution and high quality, the amount of information or bits to be transmitted increases relative to the existing image/video data, and thus, transmitting image data using a medium such as an existing wired/wireless broadband line or an existing storage medium or storing image/video data using existing storage medium increase transmission cost and storage cost.

In addition, interest and demand for immersive media such as virtual reality (VR) and artificial reality (AR) content or holograms has recently increased and broadcasting for image/video is having characteristics different from reality images such as game images has increased.

Accordingly, a highly efficient image/video compression technology is required to effectively compress, transmit, store, and reproduce information of a high-resolution, high-quality image/video having various characteristics as described above.

The present disclosure provides a method and apparatus for increasing image/video coding efficiency.

The present disclosure also provides an efficient filtering application method and apparatus.

The present disclosure also provides an efficient ALF application method and apparatus.

According to an embodiment of the present disclosure, a filtering process may be performed on reconstructed chroma samples based on reconstructed luma samples.

According to an embodiment of the present disclosure, filtered reconstructed chroma samples may be modified based on reconstructed luma samples.

According to an embodiment of the present disclosure, information on whether CCALF is available may be signaled in an SPS.

According to an embodiment of the present disclosure, information on values of cross-component filter coefficients may be derived from ALF data (normal ALF data or CCALF data).

According to an embodiment of the present disclosure, identifier (ID) information of an APS including ALF data for deriving cross-component filter coefficients in a slice may be signaled.

According to an embodiment of the present disclosure, information on a filter set index for CCALF may be signaled in units of CTUs (blocks).

According to an embodiment of the present document, a video/image decoding method performed by a decoding apparatus is provided.

According to an embodiment of the present document, a decoding apparatus for performing video/image decoding is provided.

According to an embodiment of the present document, a video/image encoding method performed by an encoding apparatus is provided.

According to an embodiment of the present document, an encoding apparatus for performing video/image encoding is provided.

According to one embodiment of the present document, there is provided a computer-readable digital storage medium in which encoded video/image information, generated according to the video/image encoding method disclosed in at least one of the embodiments of the present document, is stored.

According to an embodiment of the present document, there is provided a computer-readable digital storage medium in which encoded information or encoded video/image information, causing the decoding apparatus to perform the video/image decoding method disclosed in at least one of the embodiments of the present document, is stored.

According to an embodiment of the present document, overall image/video compression efficiency may be increased.

According to an embodiment of the present document, subjective/objective visual quality may be improved through efficient filtering.

According to an embodiment of the present disclosure, an ALF process may be efficiently performed and filtering performance may be improved.

According to an embodiment of the present disclosure, reconstructed chroma samples filtered based on reconstructed luma samples may be modified to improve picture quality and coding accuracy of a chroma component of a decoded picture.

According to an embodiment of the present disclosure, the CCALF process may be efficiently performed.

According to an embodiment of the present disclosure, ALF-related information may be efficiently signaled.

According to an embodiment of the present disclosure, CCALF-related information may be efficiently signaled.

According to an embodiment of the present disclosure, ALF and/or CCALF may be adaptively applied in units of pictures, slices, and/or coding blocks.

According to an embodiment of the present document, when CCALF is used in the encoding and decoding method and apparatus for a still image or video, filter coefficients for CCALF and the on/off transmission method in a block or CTU unit may be improved, thereby increasing encoding efficiency.

The present document may be modified in various forms, and specific embodiments thereof will be described and shown in the drawings. However, the embodiments are not intended for limiting the present document. The terms used in the following description are used to merely describe specific embodiments, but are not intended to limit the present document. An expression of a singular number includes an expression of the plural number, so long as it is clearly read differently. The terms such as “include” and “have” are intended to indicate that features, numbers, steps, operations, elements, components, or combinations thereof used in the following description exist and it should be thus understood that the possibility of existence or addition of one or more different features, numbers, steps, operations, elements, components, or combinations thereof is not excluded.

Meanwhile, each configuration in the drawings described in the present document is shown independently for the convenience of description regarding different characteristic functions, and does not mean that each configuration is implemented as separate hardware or separate software. For example, two or more components among each component may be combined to form one component, or one component may be divided into a plurality of components. Embodiments in which each component is integrated and/or separated are also included in the scope of the document of the present document.

Hereinafter, examples of the present embodiment will be described in detail with reference to the accompanying drawings. In addition, like reference numerals are used to indicate like elements throughout the drawings, and the same descriptions on the like elements will be omitted.

The present document is about video/image coding. For example, the method/embodiment disclosed in the present disclosure is a Versatile Video Coding (VVC) standard (ITU-T Rec. H.266), a next-generation video/image coding standard after VVC, or other video coding related standards (For example, it may be related to the High Efficiency Video Coding (HEVC) standard (ITU-T Rec. H.265), essential video coding (EVC) standard, AVS2 standard, etc.).

The present disclosure presents various embodiments related to video/image coding, and unless otherwise stated, the embodiments may be combined with each other.

In the present disclosure, a video may mean a set of a series of images according to the passage of time. A picture generally means a unit representing one image in a specific time period, and a slice/tile is a unit constituting a portion of a picture in coding. A slice/tile may include one or more coding tree units (CTUs). One picture may consist of one or more slices/tiles. One picture may include one or more tile groups. One tile group may include one or more tiles.

A pixel or a pel may mean a smallest unit constituting one picture (or image). Also, ‘sample’ may be used as a term corresponding to a pixel. A sample may generally represent a pixel or a value of a pixel, and may represent only a pixel/pixel value of a luma component or only a pixel/pixel value of a chroma component. Alternatively, the sample may mean a pixel value in the spatial domain, and when such a pixel value is transformed into the frequency domain, it may mean a transform coefficient in the frequency domain.

A unit may represent a basic unit of image processing. The unit may include at least one of a specific region of the picture and information related to the region. One unit may include one luma block and two chroma (e.g., Cb, cr) blocks. The unit may be used interchangeably with terms such as block or area in some cases. In a general case, an M×N block may include samples (or sample arrays) or a set (or array) of transform coefficients of M columns and N rows. Alternatively, the sample may mean a pixel value in the spatial domain, and when such a pixel value is transformed to the frequency domain, it may mean a transform coefficient in the frequency domain.

In the present disclosure, the term “/” and “,” should be interpreted to indicate “and/or.” For instance, the expression “A/B” may mean “A and/or B.” Further, “A, B” may mean “A and/or B.” Further, “A/B/C” may mean “at least one of A, B, and/or C.” Also, “A/B/C” may mean “at least one of A, B, and/or C.”

Further, in the document, the term “or” should be interpreted to indicate “and/or.” For instance, the expression “A or B” may comprise 1) only A, 2) only B, and/or 3) both A and B. In other words, the term “or” in the present disclosure should be interpreted to indicate “additionally or alternatively.”

As used herein, “at least one of A and B” may mean “only A”, “only B” or “both A and B”. In addition, in this specification, the expression “at least one of A or B” or “at least one of A and/or B” means “at least one It may be interpreted the same as “at least one of A and B”.

Also, as used herein, “at least one of A, B and C” means “only A”, “only B”, “only C”, or “A, B and C” Any combination of A, B and C”. Also, “at least one of A, B or C” or “at least one of A, B and/or C” means may mean “at least one of A, B and C”.

In addition, parentheses used herein may mean “for example”. Specifically, when “prediction (intra prediction)” is indicated, “intra prediction” may be proposed as an example of “prediction”. In other words, “prediction” in the present specification is not limited to “intra prediction”, and “intra prediction” may be proposed as an example of “prediction”. Also, even when “prediction (ie, intra prediction)” is indicated, “intra prediction” may be proposed as an example of “prediction”.

In this specification, technical features that are individually described within one drawing may be implemented individually or simultaneously.

illustrates an example of a video/image coding system to which the present document may be applied.

Referring to, a video/image coding system may include a source device and a reception device. The source device may transmit encoded video/image information or data to the reception device through a digital storage medium or network in the form of a file or streaming.

The source device may include a video source, an encoding apparatus, and a transmitter. The receiving device may include a receiver, a decoding apparatus, and a renderer. The encoding apparatus may be called a video/image encoding apparatus, and the decoding apparatus may be called a video/image decoding apparatus. The transmitter may be included in the encoding apparatus. The receiver may be included in the decoding apparatus. The renderer may include a display, and the display may be configured as a separate device or an external component.

The video source may acquire video/image through a process of capturing, synthesizing, or generating the video/image. The video source may include a video/image capture device and/or a video/image generating device. The video/image capture device may include, for example, one or more cameras, video/image archives including previously captured video/images, and the like. The video/image generating device may include, for example, computers, tablets and smartphones, and may (electronically) generate video/images. For example, a virtual video/image may be generated through a computer or the like. In this case, the video/image capturing process may be replaced by a process of generating related data.

The encoding apparatus may encode input video/image. The encoding apparatus may perform a series of procedures such as prediction, transform, and quantization for compaction and coding efficiency. The encoded data (encoded video/image information) may be output in the form of a bitstream.

The transmitter may transmit the encoded image/image information or data output in the form of a bitstream to the receiver of the receiving device through a digital storage medium or a network in the form of a file or streaming. The digital storage medium may include various storage mediums such as USB, SD, CD, DVD, Blu-ray, HDD, SSD, and the like. The transmitter may include an element for generating a media file through a predetermined file format and may include an element for transmission through a broadcast/communication network. The receiver may receive/extract the bitstream and transmit the received bitstream to the decoding apparatus.

The decoding apparatus may decode the video/image by performing a series of procedures such as dequantization, inverse transform, and prediction corresponding to the operation of the encoding apparatus.